After a bit of chasing I have managed to obtain the statistics on how active councillors have been. This spreadsheet shows how many items of casework -- raising housing issues on behalf of residents, reporting fly tipping, requesting repairs to streetlights for example, asking questions of officers on behalf of residents etc -- each councillor has put through the Front Office system in each month since the elections in May. As you can see there is a large range in the levels of activity.
As people have pointed out in the past casework is only one aspect of a councillor's work and I wouldn't expect the mayor for example to be doing much casework as he or she is busy being the figurehead of the council. But I still think it is a useful measure of how active your councillors are.